X-ray cathode



Patented Oct. 3, 1922,

SINCLAIR TOUEEY, 013 NEW YORK, N. Y.

X-RAY CAJJHODE.

Application filed August 25, 1920. fierial No. 405,824

To all whom it may concern:

Be it known that I, SINOLAIR Tousnr, a citizen of the United States, and resident of New York city, N. Y., have invented certain new and useful Improvements in X-Bay Cathodes, of which the following is speci fication.

The invention relates to that type of X.- ray apparatus in which the tube is evacuated of freegas and the cathode is heated to incandescence to produce the electrons neces sary for the production of the X-ray, such as is disclosed in certain patents of Coolidge, Lilienfeld, and an example of which is found in patent of Kelly, No. 1,285,215, November 19, 1918. In this patent a cup shaped cathode is shown in Figs. 7, 7 7", which is itself heated by the passage of a relatively heavy current to a temperature which will result in the liberation of corpuscles or negatively charged particles at the rate desired.

- Fig. l is a diagrammatic view otthe anode and cathode.

Fig. 1 is a perspective view of the cathode and the electric leads.

Figs. 2 and 8 are views of modification of the cathode.

Fig. 4 is a perspective view of another form of cathode.

F ig. 5 is a sectional view througha part of Fig. 4;. r

Fig. 6 is a view ofanother form oi cathode associated with an anode.

Figs. A, Band C are diagrams.

In carrying out my invention I raise the cathode to the required temperature by the passage through it of a relatively weak current. I do not employ a heated filament for throwing off the negatively charged particles into the vacuous space as has been done heretofore, but, as stated above, 1 heat the cathode by the passage or the current there through and I employ a cathode of such form that a relatively weak current may be employed.

This cathode as shown in the diagram, Fig. 1, is of elongated form, curved both transversely and longitudinally and might be likened in shape to the rind oi? a slice of melon or orange peel. Such a shape would be approximated by cutting a hollow sphere in parallel planes at each side of its center or poles and then taking the middle section and severing it transversely to get the desired length.

With a cup shaped form oi cathode, such as disclosed inthe Kellypatent, as above stated, a relatively heavy current is employed. while with the present improved term of cathode, only a relatively weak current is necessary to produce incandescence.

It a cup of conducting material were out lnto a number of parallel strips say from one part of the rim to the opposite part and joined together at each end, their resistance might not be verydiilercnt from that of the uncut cup. Whereas it the cutting is done in such a way that a long narrow strip is produced (like an apple peel. representing the whole apple) the resistance becomes much greater. If we talre as a unit of re s stance a single strip as long as the curved line from one part of the edge of the cup to the opposite part of the edge and as wide as one-sixth the transverse curved measurement of the cup, then the resistance of six parallel segments joined at their ends would be about one-sixth the resistance of one strip and so also would be the resistance of the uncut cup.

On the other hand, the resistance of a con tinuous strip of the same width as a single strip, but SlX times the length would be six times the resis ance 01": a single strip or thirty six times that of the uncut cup.

The electrical resistance in ohms of two identical (as to material, thickness, width and length) conducting paths a: and 3 connected in parallel as in Fig. B is half as great as the resistance of one such eonducting path alone and one quarter as great as that oi? the same two conducting paths con nected in series, as in Fig. 0.

confining our invention to Figures B-C and assuming that B has sufficient resistance to become suitably incandescent with a certain voltage. Then with C, first with the same voltage one-tourth of the current would pass. And second for the same current four times the voltage would. be required. its a matter or -tact, what would be done would be to send through the successive portions of the conducting path in C the same current (in amperes) that produces suitable incandesoence when passed through each of the two parallel conducting paths in This of course is half the total current passing through B. And to send 9; the current through 4 times the resistance would requlre two times the voltage.

In practice, if the width of the ribbon were :1; that of the Kelly cup, the current would be the number of amperes.

If with minewe should duplicate the factors for the Coolidge tube of about 41} amperes priming current then with Kellys the current would according to our calculation have to be 36-amperes. The latter relatively strong current might possibly be used for a few seconds but would overheat the conducting cords leading to and inside the X-ray tube when run for several minutes at a time, as required for X-ray treatments. This relat vely strong current could not be furnished by the 12 volt storage battery in ordinary use with the Coolidge tube for any appreciable length of time without destroying the storage battery. And the same is true of the transformer used for the Coolidge tube filament current. A storage battery for sending the relatively strong current of say 36 amperes through a resistance'inthe cup of only 1/24 ohm might consist of only one couple (not 6 couples as in an ord'nary storage battery for the purpose) and of enormous size. It could not be used for priming'a Coolidge tube. A transformer for producing this relatively strong current would also be useless for the Coolidge tube. V

There are two special factsz-One, the relativel strong current is impracticable because tiie cannot stand it on account of overheating. The voltage and amperage employed for theCoolidge tube are suitable and convenient and are in-common use and there is the same advantage in conformity to a standard source of current as in thecase of in.-

candescent bulbs for ordinary lighting, no-.

I which would be developed by cutting Zig zag or spiral shaped ribbons from a spherical cup with change in shape or position.

In Fig. 4 I show a modification of-my improved cathode in which the light lines 1, 2, indicatethe outline of a hemispherical bowl of heat resistant electrically non-conducting material upon the interior of which is mounted a band 3 of material of the same tube and its conducting wires shape at every part as the portion of the interior of the hemisphere to which it is applied.

This band of material is that defined by the heavy lines, 4, 4, and is the sole means of emitting electrons.

Omitting the faint line from this diagram we would then leave the figure as representing a ribbon or band without a backing but having the shape shown and as just described and retaining its shape only by its rigidity.

In either case the current would be applied atthe knob-like projections 5 at the ends of the ribbon and these may also form the points of support.

Instead of applying this conducting ma.- terial in the form of a band to the surface of the hemispherical body, it may be inlaid and further I may employ a rod of any cross sectional shape inlaid in heat resisting non-conducting material and get the correct hollowed surface at all parts of its length by grinding it down to coincide with and form a flush continuation of the surface of the backin in which it is inlaid which surface woul be generally of cup shape whether of exact semi-spherical or not. This is indicated diagrammatically in Fig. 5 the shaded section indicating the portion which is to be ground away.

While in the previous description I have referred to the general shape of the cathode as that which would be derived from cutting a section out of a hemisphere it will be understood that its general shape ma be that derived from a saucer-shaped bod y. Further, the ribbon while curved lengthwise 'need not necessarily be curved transversely.

It would doubtless have to be so if it were desired to focus the cathode particles upon a mathematical point, but in practice it is better to have a focus spot of considerable size, fully. as large as the probable transverse width of the ribbon and therefore, in one form of my invention, the ribbon may be described as generally curved lengthwise, and specifically either concave, slightly concave, flat, or slightly convex transversely.

I claim:

1. A cathode for X-ray apparatus comprising a ribbon-like electric conducting member curved lengthwise and also transversely and having means for passing a low tension electric current from end to end of the ribbon, substantially as described.

2. A cathode for X-ra apparatus comprising a ribbon-like electric conductin member curved lengthwise and concaved transversely on its face presented to the anode and having means for passing a low tension electric current from end to end of the ribbon, substantially as described.

3. A cathode for X-ray apparatus comprising a ribbon-like electric conducting member concaved lengthwise and transversely on its face presented to the anode and having means for passing a low tension electric current from end to end of the ribbon, substantially as described.

4. A cathode for X-ray apparatus comprising a backing of heat resisting nonconducting material of general cup shape and a strip of electrically conducting material carried thereby on its concave face and having the conducting Wires attached at its opposite ends, substantially as described.

5. An X-ray apparatus comprising in combination, a tube evacuated of free gas and a cathode to be heated to produce elec trons independent of gas ionization, said cathode comprising a ribbon like member having electric conductivity, curved in the direction or]? its length and transversely With its concave face presented to the anode, and electric leads connected With the ends o said member.

In testimony whereof I affix my signature.

SINCLAIR TOUSEY. 

